This invention relates to a monitoring circuit, and in particular to a circuit for monitoring a battery voltage, for example in a mobile communications device such as a mobile phone.
In operation of a battery-powered mobile communications device, such as a mobile phone, it is useful for a controller of the device to have information about various system parameters, such as the voltage being supplied by the battery. However, if frequent measurements are made by the controller, this requires a large number of measurements to be sent over the internal communication bus of the device, which puts an increased load on the controller, and results in higher power consumption.
U.S. Pat. No. 5,570,025 describes a cellular phone in which, during a call, battery voltage measurements are sent to a CPU for processing.
JP-11-183532 discloses a battery monitoring apparatus with an analog-digital (A/D) converter, which converts a measured battery voltage into a digital signal, and monitors the signal in cycles. The device further includes means for setting a reference voltage, and for comparing the digitized battery voltage with the reference voltage, providing an output interruption signal to the processor when the voltage drops below the reference voltage. Thus, battery monitoring is carried out independently of the processor, until the voltage falls below the preset reference voltage.
Although this system provides a warning when a battery voltage falls below a preset threshold, it does not provide any further information about the condition of the battery.
In accordance with one aspect of the invention, a monitoring device includes output registers, from which parameter values can be read by a processor unit.
Advantageously, the device makes frequent measurements, and updates parameter values on the basis of those measurements. The updated stored parameter values can then be read by the processor.
This has the advantage that the processor does not have to read a large number of values, in order to obtain the information required about the parameters. This therefore has the result that communications on the bus are reduced, and power consumption is reduced.
For example, the parameters may include a maximum battery voltage, a minimum battery voltage, and an average battery voltage.
Moreover, the monitoring device can be used as a battery monitor in a mobile communications device, such as a mobile phone. In that case, a battery voltage would be expected to change, depending on whether or not the device is transmitting. Separate output registers can therefore be provided for parameters which depend on whether or not the device is transmitting. For example, measured parameters may include a minimum battery voltage while transmitting, a minimum battery voltage while not transmitting, a maximum battery voltage while transmitting, a maximum battery voltage while not transmitting, an average battery voltage while transmitting, and an average battery voltage while not transmitting.
In addition, the monitoring device in accordance with the invention can be used to monitor a battery voltage during battery charging, the maximum battery voltage being of most importance. In that case, a charging current can also be measured, and output registers can be provided for parameters such as a maximum current, minimum current, and average current.
The monitoring device of the present invention can further allow threshold values to be set for any of the measured parameter values, and can automatically send a signal to the processor unit whenever any parameter values passes its respective threshold value.
It should be emphasised that the term xe2x80x9ccomprises/comprisingxe2x80x9d when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.